As a conventional hybrid construction machine, a known hybrid construction machine rotates a hydraulic motor using working oil introduced from a turning motor so as to perform energy regeneration.
JP2009-281525A discloses that an electromagnetic switching valve is switched to the opening position to perform turning regeneration and the degree of opening of a proportional electromagnetic throttle valve disposed in parallel to a relief valve is controlled to reduce the passage resistance of the relief valve when a pressure signal of a pressure sensor that detects a turning pressure during turning or a brake pressure during braking of the turning motor reaches a preliminarily set pressure.